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Updated: May 3, 2026
A Murine Model of Group B Streptococcus Vaginal Colonization
Published on: November 16, 2016
Variation in SeM genotype is associated with virulence of Streptococcus equi subspecies equi in mice
Marlane Geribone Seeger1, Diego Cristiano Correa1, Roberto Antônio Delgado Barcelos1
1Programa de Pós-Graduação em Medicina Veterinária, Universidade Federal de Santa Maria (UFSM), Santa Maria, RS, Brazil.
Abstract:
Strangles is a common infectious disease caused by Streptococcus equi subspecies equi (S. equi) that primarily affects the upper respiratory system. To date, 271 alleles of the M protein (seM) have been identified that may be related to antigenic differences of isolates. This study evaluated the virulence of S. equi isolates from different alleles of the M protein in an experimental mouse model. Thirty-six Swiss mice were allocated into 12 groups (G1-G12) and each infected group received a different isolate of S. equi recovered from horses with strangles: G1: seM-117; G2: seM-61; G3: seM-123; G4: seM-115; G5: seM-271; G6: seM-124; G7: seM-158, and G8: seM-39, G9: no allele, G10: seM-28, G11: control (no infection - Brazil), G12: control (no infection - Texas). Mice were infected intranasally with 2 × 106 CFU/mL and monitored for clinical signs, weight, and nasal culture over 10 days. Clinical signs varied among mice inoculated with different isolates of S. equi, ranging from lethargy, serous ocular discharge, and rhinitis to tachypnea and neurological alterations. Isolates from alleles seM-158 (G7), seM-39 (G8), and seM-271 (G5) were classified as highly virulent, frequently resulting in death or euthanasia, along with consistent bacterial excretion and enlargement of lymph nodes. Mice in G4 (seM-115), G6 (seM-124), G9 (no allele), and G10 (seM-28) showed moderately severe clinical signs of disease, whereas clinical signs for mice in G1 (seM-117), G2 (seM-61), and G3 (seM-123) were mild or absent. Results demonstrate that isolates of S. equi with different M protein alleles exhibit varying levels of virulence in mice, ranging from asymptomatic infection to severe illness and mortality. Additional investigations should be conducted to assess whether virulence in horses is associated with S. equi M protein variability and whether the association of M protein genotype with virulence is causal.
Insights
Strangles, a respiratory disease in horses, shows varying severity based on Streptococcus equi M protein alleles. This study found specific M protein alleles correlate with higher virulence and mortality in mice, suggesting a link to disease severity in horses.
Area of Science:
- Veterinary Medicine
- Microbiology
- Immunology
Background:
- Strangles is a common infectious upper respiratory disease in horses caused by Streptococcus equi subspecies equi (S. equi).
- The M protein (seM) of S. equi has 271 identified alleles, potentially influencing antigenic variation and isolate virulence.
- Understanding the relationship between seM alleles and S. equi virulence is crucial for disease management and vaccine development.
Purpose of the Study:
- To evaluate the virulence of S. equi isolates associated with different seM alleles using a mouse model.
- To determine if variations in seM alleles correlate with differential disease severity and outcomes in experimentally infected mice.
Main Methods:
- Thirty-six Swiss mice were divided into 12 groups and intranasally inoculated with different S. equi isolates, each characterized by a specific seM allele or lacking one.
- Control groups received no infection.
- Mice were monitored for clinical signs, weight changes, and bacterial excretion over 10 days post-infection.
Main Results:
- Significant variation in clinical signs and outcomes was observed among mice infected with different S. equi isolates.
- Isolates from seM alleles seM-158, seM-39, and seM-271 demonstrated high virulence, leading to mortality or euthanasia, consistent bacterial shedding, and lymph node enlargement.
- Isolates from seM-115, seM-124, seM-28, and the 'no allele' group exhibited moderate virulence, while isolates seM-117, seM-61, and seM-123 caused mild or no clinical signs.
Conclusions:
- The study demonstrates that S. equi isolates with distinct M protein alleles exhibit a range of virulence in a mouse model, from asymptomatic infections to severe disease and mortality.
- These findings suggest a potential association between M protein genotype and the virulence of S. equi.
- Further research is warranted to investigate whether this observed virulence variation in mice correlates with disease severity in horses and if the M protein genotype causally influences virulence.
